Mbms session restoration in eps for path failure

ABSTRACT

Restoration procedures in a Multimedia Broadcast Multicast Service (MBMS) network (also referred to as evolved MBMS (eMBMS) network) in case of a path failure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 14/785,202, which has asection 371(c) date of Oct. 16, 2015 and which is the national stageapplication of International Patent Application No. PCT/EP2014/057722,filed Apr. 16, 2014, which claims priority to U.S. Provisional PatentApplication Nos. 61/818,602 filed May 2, 2013 and 61/812,280 filed Apr.16, 2013. The above identified applications are incorporated by thisreference.

TECHNICAL FIELD

Embodiments herein relate generally to restoration procedures in aMultimedia Broadcast Multicast Service (MBMS) network (also referred toas evolved MBMS (eMBMS) network) in case of a path failure.

BACKGROUND

In a typical communications network a wireless device, communicates viaa Radio Access Network (RAN) to one or more Core Networks (CNs). Thecommunications network may also be referred to as e.g. a wirelesscommunications network, a wireless communications system, acommunications network, a communications system, a network or a system.

The wireless device may be a device by which a subscriber may accessservices offered by an operator's network and services outsideoperator's network to which the operator's radio access network and corenetwork provide access, e.g. access to the Internet. The wireless devicemay be any device, mobile or stationary, enabled to communicate over aradio channel in the communications network, for instance but notlimited to e.g. user equipment, mobile phone, smart phone, sensors,meters, vehicles, household appliances, medical appliances, mediaplayers, cameras, Machine to Machine (M2M) device or any type ofconsumer electronic, for instance but not limited to television, radio,lighting arrangements, tablet computer, laptop or Personal Computer(PC). The wireless device may be portable, pocket storable, hand held,computer comprised, or vehicle mounted devices, enabled to communicatevoice and/or data, via the radio access network, with another entity,such as another wireless device or a server.

The radio access network covers a geographical area which is dividedinto cell areas, with each cell area being served by a base station. Thebase station may be called a Radio Base Station (RBS), evolved NodeB(eNB), NodeB, B node, Radio Network Controller (RNC), Base StationController (BSC), Base Transceiver Station (BTS), MCE, depending on thetechnology and terminology used. A cell is a geographical area whereradio coverage is provided by the radio base station at a base stationsite. The base station communicates with the wireless device(s) withinrange of the base station.

According to the 3GPP, Multimedia Broadcast Multicast Services (MBMS)“is a point-to-multipoint service in which data is transmitted from asingle source entity to multiple recipients. Transmitting the same datato multiple recipients allows network resources to be shared.” MBMSoffers two modes: broadcast mode and multicast mode. The MBMSarchitecture enables efficient usage of radio network and core networkresources. evolved MBMS (eMBMS) may be described as the Evolved PacketCore (EPC) version of MBMS. The eMBMS evolution brings improvedperformance thanks to higher and more flexible LTE bit rates, singlefrequency network operations, and carrier configuration flexibility.

In MBMS, there are some network nodes or functional entities which areimportant. Multi-cell/multicast Coordination Entity (MCE) is a networknode or functional entity which is responsible for allocation of timeand frequency resources for MBMS transmission. The MCE may be co-locatedwith for example an eNB. Another network node is the MBMS-GW, which isthe entry point for incoming broadcast/multicast data traffic. TheMBMS-GW broadcasts data packets to all eNBs within an area. BroadcastMulticast-Service Centre (BM-SC) is a network node or functional entitywhich is necessary in order for a communications network to supportMBMS. The BM-SC is in charge of providing service to the end user.

Some of the reference points in MBMS are Sn, SGmb and Sm. Sn is thereference point for the control plane between MBMS-GW and the SGSN. SGmbis the reference point for the control plane between BM-SC and theMBMS-GW. Sm is the reference point for the control plane between theMobility Management Entity (MME) and the MBMS-GW. M3 ApplicationProtocol (M3AP) supports the M3 interface which is between the MCE andthe MBMS GW. A reference point may also be referred to as an interface.Signaling between nodes is exchanged at a reference point.

The purpose of a MBMS Session Start procedure is to request the radioaccess network to notify wireless devices about an upcoming MBMS Sessionof a given MBMS Bearer Service and to establish a MBMS Radio AccessBearer (RAB) and MBMS signalling connection for this MBMS Session. TheMBMS Session Start procedure is triggered by the core network. Forexample, the core network initiates the procedure by sending a MBMSSession Start request message to the RNC. The MBMS Session Start requestmessage comprises different parameters. The RNC acts according to thereceived MBMS Session Start request message. The RNC sends a MBMSSession Start response message or a MBMS Session Start failure messageto the core network, depending on the outcome of the procedure.

According to 3GPP, the loss or corruption of the data stored in theaforementioned network entities for support of MBMS service(s) for eachMBMS session context which are created by the MBMS Session Startprocedure and updated by the MBMS Session Update procedure willseriously degrade the MBMS service(s) offered to mobile subscribers. Itis therefore necessary to define procedures to limit the effects of suchfailure, and to restore the MBMS service with minimized impact to themobile subscribers. Such restoration procedures are related to failureand/or restart of several types of network nodes and networkpaths/interfaces, such as e.g. MBMS-GW, MME, SGSN etc. The termsrestoration and re-establishment are equivalent.

A failure may be a failure to receive a particular message, failure of ahardware or software component of a network node. A failure may befull/complete or partial. After a node has been restarted, all itsbearer contexts are deleted.

3GPP has started a new project called eMBMS restoration procedures,where the objective of this project is to specify enhanced restorationprocedures to explicitly define the EPS behavior and to enablerestoration of the eMBMS service when possible in order to minimize theend-user service impact upon different kinds of failure over the controlpath. Examples of such failures are as follows: MBMS-GW failure/restart;MME/SGSN failure/restart; MCE failure/restart; BM-SC failure/restart;Sm/Sn path failure; M3AP path failure; SGmb path failure.

It has been agreed that the principle of these restoration procedures isto try to re-establish the control path to allow a subsequent MBMSsession update and/or MBMS session stop. In addition, suchre-establishing may be performed before bringing down the MBMS sessions.But the specific procedures under various failure scenarios are stillunder discussion.

The system behaviour upon restoration of a MBMS session towards analternative downstream node during a SGmb path failure remains undefinedin current standards.

SUMMARY

An objective of embodiments herein is therefore to obviate at least oneof the above disadvantages and to provide an enhanced restorationprocedure in a communications network.

This objective is attained in a first aspect of the present invention bya method in a network node for restoring an MBMS session after pathfailure. The method comprises detecting a path failure associated withan old path between the network node and an old control plane node,which old control plane node controls at least one MBMS session, andselecting an alternative control plane node to re-establish the at leastone MBMS session. The method further comprises detecting that the oldpath between the network node and the old control plane node has beenrecovered, and sending to the old control plane node an MBMS sessionstop request in order to clear the MBMS session on the nodes along theold path involving the old control plane node.

This objective is attained in a second aspect of the present inventionby a network node configured to restore an MBMS session after pathfailure, comprising a processor and a memory, which memory containssoftware that when executed by the processor, the network node isoperative to detect a path failure associated with an old path betweenthe network node and an old control plane node, which old control planenode controls at least one MBMS session, and select an alternativecontrol plane node to re-establish the at least one MBMS session. Thenetwork node is further operative to detect that the old path betweenthe network node and the old control plane node has been recovered, sendto the old control plane node an MBMS session stop request in order toclear the MBMS session on the nodes along the old path involving the oldcontrol plane node.

This objective is attained in a third aspect of the present invention bya method in a control plane node for restoring an MBMS session afterpath failure, comprising receiving an MBMS session start request from anetwork node, and sending an MBMS session start request to an MCE. Themethod further comprises receiving an MBMS session start response fromthe MCE, and sending an MBMS session start response to the network nodeacknowledging the receipt of the MBMS session start request.

This objective is attained in a fourth aspect of the present inventionby a control plane node configured to restore an MBMS session after pathfailure, comprising a processor and a memory, which memory containssoftware that when executed by the processor, the control plane node isoperative to receive an MBMS session start request from a network node,and send an MBMS session start request to an MCE. Further the controlplane node is operative to receive an MBMS session start response fromthe MCE, and send an MBMS session start response to the network nodeacknowledging the receipt of the MBMS session start request.

This objective is attained in a fifth aspect of the present invention bya method in an MCE for restoring an MBMS session after path failurewhere the MBMS session already exists on the MCE, comprising receivingan MBMS session start request comprising a re-establishment flag for theMBMS session from an alternative control plane node, and re-establishingthe MBMS session with the alternative control plane node.

This objective is attained in a sixth aspect of the present invention byan MCE configured to restore an MBMS session after path failure wherethe MBMS session already exists on the MCE, comprising a processor and amemory, which memory contains software that when executed by theprocessor, the MCE is operative to receive an MBMS session start requestcomprising a re-establishment flag for the MBMS session from analternative control plane node, and re-establish the MBMS session withthe alternative control plane node.

Further provided are computer programs performing methods according toembodiments of the present invention, and computer program productscomprising computer readable medium having the computer programsembodied therein.

Advantageously, with restoration procedures proposed by embodimentsdescribed herein, re-establishment of the control path is facilitated toallow a subsequent MBMS session update and/or MBMS session stop orsimilar. In addition, such re-establishment may advantageously beperformed before bringing down the MBMS sessions.

A restoration flag is preferably set by the node who initiates arestoration procedure with re-selection of a downstream control node,e.g. the BM-SC selects an alternative MBMS-GW or the MBMS-GW selects analternative MME. The restoration flag may be set and/or used togetherwith a timer and/or a counter.

The timer may be set to the Max non-transient path failure timer node inthe node (who initiates the restoration procedure) minus the timeelapsed since the path failure is detected up to the moment when thereselection of the alternative control path, and addition of thedifference between the Max non-transient path failure in the node (whoinitiates the restoration procedure) and the next downstream node. Thecounter is incremented if there is a subsequent path failure where thesame node initiates the restoration procedure.

The restoration flag may be included in the MBMS session start requestmessage or similar as long as the associated timer has not expired whena subsequent downstream failure takes place, e.g. during a Sm failure.An alternative MME may receive the MBMS session start request messagetogether with at least one of a restoration flag, a timer and counter,before the timer expires. If there is a MCE restart and in order tore-establish the MBMS session, the MME may send the MBMS session startrequest message together with a restoration flag.

The receiving node may use the restoration flag together, possiblytogether with an associated timer and/or counter, to decide which MBMSSession Start message or similar may be accepted for the case that thesame MBMS session is controlled by two or more different control plannodes, e.g. MME/SGSN/MBMS-GW.

The receiving node may use the restoration flag together with anassociated timer and/or counter, IP address of old control node, anindication if it is the first node in the restoration path, to decide ifit should send a delete message to delete the MBMS session which becomesoutdated in the old node.

The situation that the same MBMS session exists in more than one controlpath should be avoided, i.e. the MBMS session in the old control pathshould be deleted. It may be required for the node who initiatesrestoration with re-selection of an alternative downstream node toinform the old node to stop the MBMS sessions which have been taken overby the alternative node after a transient path failure is recovered. Acontrol path is a path in which the control information is transmittedin the communications network. As an alternative, it may be requiredthat the first downstream node informs the same type of network entity,i.e. the same level controlling node in the MBMS network, for example,at SGmb path failure, once the MBMS-GW2 receives a MBMS session startmessage with a restoration flag together with the old MBMS-GW 1 addressand with an indication which indicates that this MBMS-GW is the firstdownstream node upon the restoration control path. Then the MBMS-GW2informs the MBMS-GW1 that the MBMS session has been taken over. Asanother example, at Sm failure, once the MME/SGSN2 receives MBMS sessionstart message with a restoration flag together with the old MME/SGSN 1address, and an indication which indicates this MME/SGSN is the firstdownstream node upon the restoration control path, then the MME/SGSN 2informs MME1 that the MBMS session has been taken over.

The embodiments herein relating to restoring a session is presented bydescribing the node behaviors clearly upon various combinations of therestoration flag (a new flag over SGmb (3GPP TS 29.061), Sm/Sn (to beadded in 3GPP TS 29.274), M3, M2 and Iu interface (to be added in 3GPPTS 25.413)) and other parameters.

The restoration flag may tell the receiver (e.g. MME/SGSN) this is arestoration procedure for the very same MBMS service identified by TMGIand Flow-ID.

If the same downstream node, e.g. MME/SGSN 1, is selected during therestoration procedure, by comparing the “MBMS IP Multicast Distribution”with the existing session information, the MME/SGSN 1 may get to knowthe Control information for the M1 interface changes or not. If itchanges, then the MME/SGSN must convey this updated information to theRAN node. If it does not change, the M3 interaction is not needed if allother parameters are the same. The M1 interface is a pure user planeinterface. A MBMS-GW is connected to multiple eNBs through M1 interfacefor data distribution. M3 and M2 are pure control plane interfaces. M3is between the MME and MCE and mainly carries MBMS session managementsignaling. A MCE is connected to one or more eNBs within the same MBMSFNthrough the M2 interface mainly for MBMS session management signalingand radio configuration signaling.

If a different downstream node, e.g. the MME/SGSN2, is selected, thenboth the old control plane node and the new control plane node will havethe same MBMS session. The embodiments herein propose to stop theresource on the old control path by the upstream node (e.g. BM-SC whoselects a new MBMS-GW in case of SGmb path failure, or MBMS-GW whoselects a new MME in case of Sm path failure) after the old path isrecovered.

Embodiments herein afford many advantages, of which a non-exhaustivelist of examples follows.

An advantage of the embodiments herein may be that by using therestoration flag along the new path, all the nodes involved may clearlydifferentiate the restoration procedure from other procedures, thusbeing able to cope with different path failure scenarios.

Another advantage of the embodiments herein may be that by introducingthe mechanism to allow the node which reselects alternative nodes duringa MBMS Session restoration procedure to release/stop a MBMS Sessionresource in the old control plane nodes once the path is recovered. Thissolves the problem with having two substantially identical or at leastclosely related MBMS Sessions' co-existing on two nodes (e.g. two GWs,two MMEs).

The embodiments herein are not limited to the features and advantagesmentioned above. A person skilled in the art will recognize additionalfeatures and advantages upon reading the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will now be further described in more detail inthe following detailed description by reference to the appended drawingsillustrating the embodiments and in which:

FIG. 1 is a schematic block diagram illustrating embodiments of acommunications network.

FIGS. 2A-C are signaling diagrams illustrating embodiments of a methodin a communications network.

FIG. 3 is a schematic block diagram illustrating embodiments of acommunications network.

FIG. 4 is a schematic block diagram illustrating embodiments of acommunications network where a Sn/Sm path failure occurs.

FIG. 5 is a schematic block diagram illustrating embodiments of acommunications network where a SGmb path failure occurs.

FIG. 6A and FIG. 6B are signaling diagrams illustrating embodiments ofMBMS Session restoration when a SGmb path failure occurs.

FIG. 7 is a signaling diagram illustrating embodiments of MBMS Sessionrestoration when a Sn/Sm path failure occurs.

FIG. 8 is a schematic block diagram illustrating embodiments of acommunications network.

FIG. 9 is a schematic block diagram illustrating embodiments of anetwork node.

FIG. 10 is a schematic block diagram illustrating embodiments of acontrol plane node.

FIG. 11 is a schematic block diagram illustrating embodiments of a RANnode.

The drawings are not necessarily to scale and the dimensions of certainfeatures may have been exaggerated for the sake of clarity. Emphasis isinstead placed upon illustrating the principle of the embodimentsherein.

DETAILED DESCRIPTION

As mentioned above, the network behaviour upon an SGmb and/or Sn/Sm pathfailure remains undefined in current standards. During the path failureover any of the Sm/Sn/SGmb interfaces, the selection of an alternativecontrol path may take place. The embodiments herein aim for providinganalysis to such path failure scenarios:

The expected behavior of a downstream node, e.g. the RNC/MCE for a Sn/Smfailure, or the MME/SGSN for a SGmb path failure when it receive therequest to restore an existing MBMS session, especially when the pathtowards an upstream node is still active.

How the resource allocated in the nodes in the old control path forthose MBMS session which have been taken over may be released.

FIG. 1 depicts a communications network 100 in which embodiments hereinmay be implemented. The communications network 100 may in someembodiments apply to one or more radio access technologies such as forexample Long Term Evolution (LTE), LTE Advanced, Wideband Code DivisionMultiple Access (WCDMA), Global System for Mobile Communications (GSM),or any other Third Generation Partnership Project (3GPP) radio accesstechnology, or other radio access technologies such as WLAN.

The communications network 100 comprises a network node 101. The networknode 101 may be a BM-SC or a MBMS-GW. The network node 101 is connectedto at least one of an old control plane node 103 a and a new controlplane node 103 b. The old node may be indicated using the letter a orthe number 1, and the new node may be indicated using the letter b orthe number 2. The term “old” refers to a node which has been previouslyused and the term “new” refers to a node which will be used in thefuture. The network node 101 may be connected to an old node and thenchange to be connected to a new node. The old control plane node 103 amay also be referred to as a first control plane node and the newcontrol plane node 103 b may also be referred to as a second controlplane node. The old control plane node 103 a may be a MBMS-GW or aMME/SGSN. The new control plane 103 b may be a MBMS-GW or a MME/SGSN.The term MME/SGSN refers to a MME or a SGSN or a co-located MME/SGSN.The old control plane node 103 a controls a number of MBMS sessions.After a path failure between the network node 101 and the old controlplane node 103 a, the network node 101 selects an alternative or newcontrol plane node, i.e. the new control plane node 103 b tore-establish the MBMS sessions. Thus, the control information, i.e.signaling, is conveyed over a new path instead of the old path.

A control plane node is a node which carries control information, alsoknown as signaling. As a contrast, a user plane node carries thenetwork's user traffic.

The communications network 100 comprises a RAN node 105 connected to theold control plane node 103 a and a new control plane node 103 b. The RANnode 105 is directly connected to the old control plane node 103 a andthe new control plane node 103 b or it is connected to the old controlplane node 103 a and the new control plane node 103 b via other old andnew control plane nodes (not shown). The RAN node 105 may be a basestation such as a NodeB, an evolved NodeB (eNB), a Radio NetworkController (RNC), a Multi-cell/Multicast Coordination Entity (MCE), orany other network unit capable to communicate over a radio carrier witha wireless device 110 being present in a cell.

The wireless device 110 may be a device by which a subscriber may accessservices offered by an operator's network and services outsideoperator's network to which the operators radio access network and corenetwork provide access, e.g. access to the Internet. The wireless device110 may be any device, mobile or stationary, enabled to communicate overa radio channel in the communications network, for instance but notlimited to e.g. user equipment, mobile phone, smart phone, sensors,meters, vehicles, household appliances, medical appliances, mediaplayers, cameras, Machine to Machine (M2M) device or any type ofconsumer electronic, for instance but not limited to television, radio,lighting arrangements, tablet computer, laptop or Personal Computer(PC). The wireless device 110 may be portable, pocket storable, handheld, computer comprised, or vehicle mounted devices, enabled tocommunicate voice and/or data, via the radio access network, withanother entity, such as another wireless device or a server.

The network node 101 is connected (directly or via another node) to acontent provider 115 which broadcasts services to the wireless device110.

It should be noted that the communication link between the network nodesmay be of any suitable kind including either a wired or wireless link.The link may use any suitable protocol depending on type and level oflayer (e.g. as indicated by the OSI model) as understood by the personskilled in the art.

In the communications network 100, the term downstream refers to thedirection from a content provider 115 to the wireless device 110. So,the old and new control plane nodes 103 a, b and the RAN node 105 may beseen as downstream nodes.

The method for session restoration after a path failure, according tosome embodiments will now be described with reference to the signalingdiagram depicted in FIG. 2A, FIG. 2B and FIG. 2C. The steps 201 a-207 ain FIG. 2A is performed first, then the steps 208 b-211 b in FIG. 2B orthe steps 208 c-218 c in FIG. 2C is performed. As an alternative to thesteps 208 b-211 b, the steps 208 c-218 c in FIG. 2C is performed. FIG.2A describes the session restoration phase. FIG. 2B describes thesession stop procedure to delete the resource for those MBMS sessionshave been relocated to an alternative control path. FIG. 2C describes analternative procedure to the procedure described in FIG. 2B where thefirst downstream control plane node deletes the resource on the oldcontrol plane path when it receives a MBMS session start request messagewith at least one of a restoration flag, IP address of the old controlnode and an indication to indicate that it is the first downstream node.

At start of the method, a MBMS session exists on the network node 101,the old control plane node 103 a and the RAN node 105, and possibly alsoon another old control plane node (not shown).

The method comprises the following steps, which steps may as well becarried out in another suitable order than described below.

Step 201 a

This step is seen in FIG. 2A. The network node 101 detects a pathfailure associated with the path between the network node 101 and theold control plane node 103 a. The path failure may be a transient pathfailure, which will be described in more detail below. As mentionedabove, the old control plane node 103 controls at least one MBMSsession.

Step 202 a

This step is seen in FIG. 2A. The network node 101 selects a new controlplane node 103 b to re-establish the MBMS session that has failed. Theselection of the new control plane node 103 b may take place before apath failure timer has expired and/or it may take place after havingreceived a session update or stop request from a content provider 115.The failure may be a Sn/Sm path failure if the network node 101 is aMBMS-GW and the old control plane node 103 a and the new control planenode 103 b are MME/SGSNs. The failure may be a SGmb path failure if thenetwork node 101 is a BM-SC and the old control plane node 103 a and thenew control plane node 103 b are MBMS-GWs.

Step 203 a

This step is seen in FIG. 2A. The network node 101 sends a MBMS sessionstart request to the new control plane node 103 b. The MBMS sessionstart request comprises at least one of a restoration flag a timer and acounter for the failed MBMS session. The purpose of restoration flag isto allow the RAN node 105 or the new control plane node 103 b to acceptthe MBMS Session Start request message for the very same service asbefore the failure. The restoration flag is needed as the RAN node 105or the new control plane node 103 b needs to differentiate whether it isan error (so it may reject it) or whether it is a restoration procedure(so it may accept it).

Step 204 a

This step is seen in FIG. 2A. The new control plane node 103 b sends theMBMS session start request comprising at least one of the restorationflag, the timer and the counter to the RAN node 105. The MBMS sessionstart request may be sent directly to the RAN node 105 or it may be sentto the RAN node 105 via another old control plane node (now shown).

Step 205 a

This step is seen in FIG. 2A. When the RAN node 105 receives therestoration flag, it knows that it may accept the MBMS session startrequest. As a consequence, the RAN node 105 stops the MBMS sessionrelated to the old control plane node 103 a and re-establishes the MBMSsession with the new control plane node 103 b from which the restorationflag was received.

Step 206 a

This step is seen in FIG. 2A. The RAN node 105 sends a MBMS sessionstart response message to the old control plane node 103 b.

Step 207 a

This step is seen in FIG. 2A. The new control plane node 103 b sends aMBMS session start response to the network node 101 acknowledgingreceipt of the request in step 203 a.

Thus, the MBMS session exists on the network node 101, the old controlplane node 103 a, the new control plane node 103 b and the MCE. The MBMSsession may also exists on another old control plane node (not shown).

The steps of FIG. 2B will now be described. The steps of FIG. 2B arealternatives to the steps show in FIG. 2C. In FIG. 2B, the node whoinitiates restoration procedure is able to stop the MBMS session in theold control plane node 103 a.

Step 208 b

This step is seen in FIG. 2B. The network node 101 detects that the pathbetween the network node 101 and the old control plane node 103 a hasbeen recovered.

Step 209 b

This step is seen in FIG. 2B. The network node 101 sends a MBMS sessionstop request or a new GTP message for the same purpose for the MBMSsession to the old control plane node 103 a in order to clear the MBMSsession on the nodes along the old path. The old path is the path thatinvolves the old control plane node 103 a. The MBMS session stop messagemay be further forwarded to the old MME/SGSN if the old control planenode 103 a is a MBMS-GW. GTP is short for General packet radio serviceTunnelling Protocol.

Step 210 b

This step is seen in FIG. 2B. The old control plane node 103 a sends aMBMS session stop response or a new GTP message for the same purpose tothe network node 101 to acknowledge the receipt of the request which wasreceived in step 209 b.

Step 211 b

This step is seen in FIG. 2B. The old control plane node 103 a handlesthe MBMS session stop request for the MBMS session. As a result of thehandling of the MBMS session stop request, the MBMS session along theold path is cleared since the MBMS session is taken over by the newcontrol plane node 103 b. The handling of the MBMS session stop requestis different depending on which node the old and new control plane nodesare and depending on their behavior. These differences will be describedin more detail below with reference to FIG. 6B. After steps 208 b-211 bhas been performed, the MBMS session only exists on the network node101, the new control plane node 103 b and the RAN node 105. In someembodiments, the MBMS session also exists on another control plane node(not shown). Thus, the MBMS session only exists along the new path. Thenew path is the path that involves the new control plane node 103 b.

The steps of FIG. 2C will now be described. The steps of FIG. 2C arealternatives to the steps show in FIG. 2B. FIG. 2C describes that thenewly selected control plane node is able to delete the resourceallocated for the given MBMS session in the old node (same type ofnode), e.g. if a MBMS GW is selected, it should send a delete message tothe old MBMS-GW.

Step 208 c

This step is shown in FIG. 2C. A MBMS session update is performed alongthe new control path involving the new control plane node 103 b.

Step 209 c

This step is seen in FIG. 2C. The network node 101 detects that the pathbetween the network node 101 and the old control plane node 103 a hasbeen recovered.

Step 210 c

This step is seen in FIG. 2C. The network node 101 selects a new controlplane node 103 b.

Step 211 c

This step is seen in FIG. 2C. The network node 101 sends a MBMS sessionstart request to the new control plane node 103 b. The MBMS sessionstart request comprises at least one of a restoration flag, the IPaddress of the old control plane node 103 a and an indication toindicate that the new control plane node 103 b is the first downstreamnode which is required to delete the resource on the old control planepath for those MBMS session which have been reallocated on the newcontrol plane node 103 b. The IP address of the old control plane node103 a makes it possible for the new control plane node 103 b to send adelete message to the old control plane node 103 a. The purpose ofrestoration flag is to allow the RAN node 105 or the control plane nodeto accept the MBMS Session Start request message for the very sameservice as before the failure. The restoration flag is needed as the RANnode 105 or the control plane node needs to differentiate whether it isan error (so it may reject it) or it is a restoration procedure (so itmay accept it).

Step 212 c

This step is seen in FIG. 2C. The new control plane node 103 b sends theMBMS session start request comprising at least one of the restorationflag, a timer and a counter to the RAN node 105. The MBMS session startrequest may be sent directly to the RAN node 105 or it may be sent tothe RAN node 105 via another old control plane node (now shown).

Step 213 c

This step is seen in FIG. 2C. When the RAN node 105 receives therestoration flag, it knows that it may accept the MBMS session startrequest. As a consequence, the RAN node 105 stops the MBMS sessionrelated to the old control plane node 103 a and re-establishes the MBMSsession with the new control plane node 103 b from which the restorationflag was received.

Step 214 c

This step is seen in FIG. 2C. The RAN node 105 sends a MBMS sessionstart response message to the network node 103 b.

Step 215 c

This step is seen in FIG. 2C. The new control plane node 103 b sends aMBMS session start response to the network node 101 acknowledgingreceipt of the request in step 211 c.

Step 216 c

This step is seen in FIG. 2C. The new control plane node 103 b sends aMBMS session stop request to the old control plane node 103 a. The MBMSsession stop request comprises an indication to indicate that the deleteis part of a restoration procedure or a new GTP message for the samepurpose for deleting the MBMS session in order to clear the MBMS sessionon the nodes along the old path. The MBMS stop message may be furtherforwarded to the old MME/SGSN if the old control plane node 103 a is aMBMS-GW.

Step 217 c

This step is seen in FIG. 2C. The old control plane node 103 a sends aMBMS session stop response or a new GTP message for the same purpose tothe network node 103 b to acknowledge the receipt of the request whichwas received in step 216 c.

Step 218 c

This step is seen in FIG. 2C. The old control plane node 103 a handlesthe MBMS session stop request for the MBMS session. As a result of thehandling of the MBMS session stop request, the MBMS session along theold path is cleared since the MBMS session is taken over by the newcontrol plane node 103 b. The handling of the MBMS session stop requestis different depending on which node the old and new control plane nodesare and depending on their behavior. These differences will be describedin more detail below with reference to FIG. 6B. After steps 208 c-218 chas been performed, the MBMS session only exists on the network node101, the new control plane node 103 b and the RAN node 105. In someembodiments, the MBMS session also exists on another control plane node(not shown). Thus, the MBMS session only exists along the new path, i.e.the path involving the network node 101, the new control plane node 103b and the MCE.

FIG. 3 depicts an embodiment of the communications network 100 forE-UTRAN access deployment. The embodiment shown in FIG. 3 is asimplified eMBMS network.

It is assumed that there are 8 different MBMS sessions broadcasted inthe network 100, which are shared among the same type of control planeentities, e.g. between MME/SGSN1 and between MBMS-GWs, to allow loadsharing. The network 100 comprises three Multi-cell/multicastCoordination Entities (MCE): MCE 1, MCE 2 and MCE 3. The MCEs in FIG. 3corresponds to the RAN node 105 in FIG. 1. All 8 active MBMS sessionsare broadcasted in MCE 1, 2 and 3 simultaneously. Each of the MCEs areconnected to two Mobility Management Entities (MME/SGSNs), i.e. MME/SGSN1 and MME/SGSN 2. The MME/SGSNs in FIG. 3 may also be a SGSN or aco-located MME/SGSN. Each of the two MME/SGSNs is connected to twoMultimedia Broadcast Multicast Service Gateways (MBMS-GWs), i.e. MBMS-GW1 and MBMS-GW 2. The active MBMS sessions for MBMS-GW1 are session 1, 2via MME/SGSN 1 and session 3, 4 via MME/SGSN 2. The active MBMS sessionsfor MBMS-GW2 are sessions 5, 6 via MME/SGSN 1 and sessions 7, 8 viaMME/SGSN 2. The MBMS-GW 1 and the MBMS-GW 2 are both connected to aBroadcast Multicast-Service Centre (BM-SC). The active MBMS sessions forthe BM-SC are sessions 1, 2, 3, 4 via the MBMS-GW1 and sessions 5, 6, 7,8 via MBMS-GW2. Note that the network 100 may comprise any othersuitable number of MCEs, MME/SGSNs, MBMS-GW and BM-SCs than shown inFIG. 3. The MME/SGSN 1 and the MME/SGSN 2 or the MBMS-GW 1 and MBMS-GW2in FIG. 3 may correspond to the old control plane node 103 a and the newcontrol plane node 103 b in FIG. 1. The MBMS-GW1 or the BM-SC in FIG. 3may correspond to the network node 101 in FIG. 1.

In the following, the terms eMBMS and MBMS may be interchangeable used.

In eMBMS, for the path failure over any of the Sm or Sn or SGmbinterfaces, the selection of an alternative/new control path may takeplace. Thus, the method for how to setup and/or update MBMS Sessionsalong the new path and how to stop the MBMS Sessions on the old pathneeds to be clearly described.

The embodiments herein aim for providing proposals on solving at leastthe following two questions: (1) How the network nodes, including atleast one of the RNC/MCE(eNB) MME/SGSN, the MBMS-GW and the BM-SC, mayreact on the MBMS6a Session start request to restore an existing MBMSsession for at least one of the Sm and Sn and SGmb path failure. (2) Howthe resource(s) allocated in the network nodes in the old control pathmay be released.

MME/SGSN, RNC/MCE Behaviour for Sn/Sm Failure

FIG. 4 illustrates and example of the behavior of the MME/SGSN and theRNC/MCE when a failure in the Sn/Sm path occurs. In FIG. 4, the networknode 101 of FIG. 1 is represented by the MBMS-GW1, the old control planenode 103 a of FIG. 1 is represented by the MME/SGSN1, the new controlplane node 103 b of FIG. 1 is represented by the MME/SGSN2 and the RANnode 105 of FIG. 1 is represented by three MCEs. In the followingexample shown in FIG. 4, it is assumed that before the Sm failure, theMME/SGSN 1 controls MBMS sessions 1, 2, 5 and 6. Then there is a Sm pathfailure between the MME/SGSN 1 and the MBMS-GW1, indicated with a starin FIG. 4. It is also assumed that a Maximal Sm path failure timerconfigured in the MME/SGSN is 120 seconds. The same timer configured inthe MBMS-GW is 115 seconds. The shorter latter timer is to re-establishcontrol path before bringing down the MBMS session.

The re-selection of the MME/SGSN may take place before or after theMaximal Sm path failure timer in the MBMS-GW expires:

(A) If the re-selection takes place after the Maximal Sm path failuretimer expires, it may be regarded as a non-transient failure and the newMME/SGSN 2 will take over the MBMS sessions 1 and 2. The old MME/SGSN1will delete all affected MBMS sessions 1 and 2. But there is a smallrisk related to this since both the old MME/SGSN1 and new MME/SGSN2 havethe same MBMS sessions (1 and 2) for 20 seconds due to the differencebetween the Maximal Sm path failure timer configured in the MME/SGSN andthe same timer configured in the MBMS-GW.

(B) However, if the re-selection takes place before the timer expired,i.e. when the path failure is regarded as a transient failure, if theMBMS-GW1 received MBMS Session update for MBMS session 1 at 30 seconds,the MBMS-GW1 tries to re-establish the control path by selecting theMME/SGSN 2. The MME/SGSN 2 will then send the MBMS session start requestmessage for MBMS session 1 to the MCEs 1, 2 and 3.

Afterwards, there will be two cases, the Sm path failure becomes anon-transient path failure; the Sm link recovers before the timerexpires, i.e. MBMS session 2 will be kept by MME/SGSN 1, while the MBMSsession 1 has been taken over by the MME/SGSN 2. For both cases, theMBMS sessions taken over by other MME/SGSN may be deleted in the oldMME/SGSN i.e. the MBMS Session 1 should be deleted in the MME1.

Conclusion: for both scenarios A and B, there are two issues.

(Issue 1) The situation where both the old MME/SGSN and new MME/SGSNhave the same MBMS session needs to be solved. This is because if one ofthe three MCEs restarts, both MME/SGSNs will try to re-establish theMBMS Session.

(Issue 2) The MCE/RNC may be allowed to differentiate a restorationprocedure from a normal error scenario, e.g. a ghost message due to atransmission problem. Especially, as specified in the 3GPP specificationTS 25.413, V. 11.3.0, it has explicitly required in the clause 8.36.4that the RNC may reject the MBMS session start request from another SGSNif the MBMS session is already controlled by an SGSN, that means thereis a valid error scenario.

To solve issue 1:

(1) A first alternative may be to let the MCEs send a RESET message witha takeover indication to the MME/SGSN 1 as long as the MCEs accept thatthe new MME/SGSN has taken over the control path. A drawback of this maybe that, before receiving all RESET messages from the MCE(s), theMME/SGSN 1 cannot immediately delete the MBMS session. Instead theMME/SGSN 1 may set the MBMS session as “invalid” upon receiving thefirst Reset, and start a timer. The timer may be a guard timer. Beforethe timer expires, the MME/SGSN may not restart the MBMS Session uponreceiving the Reset or M3 Setup from any MCE, e.g. due to a M3 pathfailure or a MCE failure. After the timer has expired, the MME/SGSN maythen remove the MBMS Session and send a MBMS Session Stop Request tothose MCEs which have not sent a RESET message with a takeoverindication, as some of MCEs may not accept the MBMS Session StartRequest message from the alternative MME/SGSN2. A drawback of thisembodiment may be that it may complicate the MME/SGSN implementation,especially when distributed mode applies, where the MCE is co-locatedwith the eNB. This leads the timer to be difficult to predict.

(2) A second alternative which solves issue 1 is that the MBMS-GWinforms the MME/SGSN 2 to delete the MBMS Session 1 in the MME1 as theMBMS session 1 has been relocated in the MME/SGSN 2, by including atleast one of a restoration flag, an IP address of the MME/SGSN 1 and anindication to require MME/SGSN 2 to delete the MBMS session on the oldMME/SGSN 1 in the MBMS Session Start Request message. If the path isrecovered before the timer expires, the MBMS-GW deletes the MBMSsessions which have been taken over by another MME/SGSN. A risk here maybe that both the old MME/SGSN and the new MME/SGSN may have the sameMBMS session between the time when the MBMS session is being taken overand the time when the Sm path is recovered.

(3) A third alternative which solves issue 1 is that when MME/SGSN2receives MBMS Session start request message with at least one of arestoration flag, the IP address of the old MME/SGSN and an indicationto indicate that this MME/SGSN should delete the resource allocated inthe old MME/SGSN for the MBMS session that has been relocated by theMBMS-GW1 on the MME/SGSN 2. After the MME/SGSN2 has received theacknowledgement as result of the MBMS session start request message, theMME/SGSN 2 send a MBMS session stop message with an indication toindicate the delete is part of restoration procedure or a new GTPmessage for the same purpose to delete the MBMS session which has beenrelocated to the MME/SGSN 2 on the old MME/SGSN 1.

To solve issue 2:

(1) The MCE/RNC needs a restoration flag comprised in the MBMS SessionStart Request message to differentiate that this is a restorationprocedure, with a possible changed parameter, the MCE/RNC should acceptit.

MME/SGSN Behaviour for SGmb Path Failure

The MME/SGSN behavior for a SGmb path failure is exemplified in FIG. 5.In FIG. 5, the network node 101 of FIG. 1 is represented by the BM-SC,the old control plane node 103 a of FIG. 1 is represented by theMBMS-GW1, the new control plane node 103 b of FIG. 1 is represented bythe MBMS-GW2 and the RAN node 105 of FIG. 1 is represented by threeMCEs. In FIG. 5, it is assumed that before the SGmb path failure, theMBMS-GW 1 is controlling MBMS sessions 1, 2, 3 and 4. And then there isa SGmb path failure between the BM-SC and the MBMS-GW 1 as indicatedwith a star in FIG. 5.

When the BM-SC has detected the SGmb path failure and if it receives aMBMS Session update or a stop request from a content provider 115 duringa transient path failure, the BM-SC may select an alternative MBMS-GW toreestablish MBMS sessions.

For example, during this period, the MBMS sessions 1 and 2 needs to beupdated. The BM-SC selects the MBMS-GW 2, and the MBMS GW2 selects theMME/SGSN 1 for the MBMS session 1 and selects the MME/SGSN 2 for theMBMS session 2.

There may be two issues, which are similar to the ones described for theSn/Sm failure in FIG. 4 above:

Issue 3: MBMS session 1 is currently controlled by the MME/SGSN 1. Nowit receives another MBMS session start request from another MBMS-GW whohas to newly allocate both the Common-Tunnel Endpoint ID (C-TEID) andthe Internet Protocol (IP) multicast address. With the different IPMulticast Source Address, should the MME/SGSN accept the request orshould it reject it? I.e. should it treat it as an error (it could be anerror due to poor transportation network, e.g. ghost message)? Ifaccepted, should it only respond to the MBMS-GW with a successful MBMSSession Start Response message or should the MME/SGSN convey the updatedControl information for the M1 interface (C-TEID, IP multicastaddresses) along the control plane interfaces (M3, M2) to the eNB?

Issue 4: There will be a risk that both MBMS-GWs have the same MBMSsession. Therefore, it would be problematic if there is a subsequentSm/Sn/M3/Iu failure because two MBMS-GWs may then try to re-establishthe MBMS session. So the MBMS session in the old MBMS-GW may be deletedas soon as the MBMS session has been taken over by another MBMS-GW.

Issue 3 is applicable for the case that a new MME/SGSN is selected incase of a Sm failure. There may be a risk that the same MBMS sessionexists in two MME/SGSNs at the same time. So, if there is another M3APpath failure or a MCE failure, both MME/SGSNs will try to re-establishthe MBMS session.

For the issue 3, if the MME/SGSN 1 obtains a restoration flag in theMBMS Session Start Request with a “MBMS IP Multicast Distribution”updated, it may overwrite the existing MBMS session towards the MBMS-GW1and send a new MBMS Session start message towards the MCEs together withthe restoration flag.

If it is the MME/SGSN 2 that receives the MBMS Session Start Requestfrom the MBMS-GW 2 together with a restoration flag, e.g. for MBMSSession 2 in this example, as there is no existing MBMS Sessionsidentified by the Temporary Mobile Group Identity (TMGI) and Flow-ID, itmay handle it as a new MBMS Session and send it to the MCEs but togetherwith the restoration flag. A TMGI uniquely identifies an MBMS bearer,which transports a MBMS service. The TMGI is structured in a way that itis possible to define a unique TMGI for a particular service withinevery network.

Inclusion of the restoration flag helps the MCE/RNC to know that it is arestoration procedure and to accept the MBMS Session start requestmessage from a MME/SGSN other than the current ones. This may solve alsothe issue 2 described with reference to FIG. 4 above.

For issue 4, apparently an embodiment using the first alternative whichuses a RESET with a take-over indication as described in in relation tothe first alternative in FIG. 4 would not work for the SGmb pathfailure, as there is no similar message to allow the MME/SGSN to informthe old MBMS-GW.

Using the second alternative by letting the MBMS-GW2 send a MBMS stopmessage to the MBMS-GW1 to delete the MBMS Session 1 will work.

The embodiment, described in in relation to the third alternative inFIG. 4 will work. The embodiment in FIG. 4 describes to let the node whoreceives MBMS session start request message with at least one of therestoration flag, the IP address of the old MME and an indication toindicate this network node should delete the resource allocated in theold network node for the MBMS session which has been relocated. So inthis case, the MBMS-GW2 may stop the MBMS Session 1 and 2 in theMBMS-GW1.

The embodiment described in in relation to the second alternative inFIG. 4 may work. The embodiment in FIG. 4 describes to let the node whoinitiates restoration with re-selection of control plane node to informthe old control plane node in order to delete the MBMS session have beentaken over by others. In this case, the BM-SC may stop the MBMS Session1 and 2 in the MBMS-GW1.

In the scenario exemplified in FIG. 5, when the BM-SC has detected aSGmb path failure and it receives a MBMS Session update or stop requestfrom the content provider 115 during a transient path failure, itselects an alternative MBMS-GW to reestablish MBMS sessions prior toperforming the MBMS update or stop request.

In FIGS. 2A, 2B and 2C above, the signaling sequence was described ingeneral. A signaling sequence for restoration in an example with a SGmbpath failure will now be described with reference to FIGS. 6A and 6B andwith reference to FIG. 5 illustrating the communications network 100where the failure occurs. The signaling sequence starts in FIG. 6B andcontinues in FIG. 6B.

FIG. 6A will now be described. MBMS Session 1 exist on BM-SC, GW1,MME/SGSN1 and MCE (eNB). FIG. 6A comprises steps 601-615 and describes aMBMS Session Restoration Phase, which steps may be performed in anysuitable order than described below:

Step 601

This step corresponds to step 201 a in FIG. 2A. A path failure occursbetween the BM-SC and the MBMS-GW 1, i.e. a SGmb patch failure.

Step 602

The content provider 115 sends a MBMS session update request for MBMSsession 1 to the BM-SC.

Step 603

This step corresponds to step 202 a in FIG. 2A. The BM-SC chooses analternative/new MBMS-GW2 and restores the MBMS Session.

Step 604

This step corresponds to step 203 a in FIG. 2A. The BM-SC sends aRe-Authorize Request (RAR) to the MBMS-GW2. The RAR may be a MBMSSession start request comprising a restoration flag for MBMS Session 1.

Step 605

The MBMS-GW 2 sends a Re-Authorize Answer (RAA) back to the BM-SC. TheRAA is a response to the RAR. The RAA may be a MBMS Session startresponse comprising an indication indicating that the MBMS Session startrequest in step 604 was ok.

Step 606

The MBMS-GW 2 sends a MBMS Session start request to the MME/SGSN 1. TheMBMS Session start request comprises the restoration flag for MBMSSession 1 and the MBMS IP multicast distribution for GW2. Note that itis also possible that the MME/SGSN 2 is selected instead of the MME/SGSN1 in this step. However, selection of MME/SGSN 1 is used as an example.

Step 607

The MME/SGSN 1 updates the MBMS Session's GTP-C path from theMME/SGSN1-GW1 to the MME/SGSN1-GW2.

Step 608

The MME/SGSN 1 sends a MBMS Session start response to the MBMS-GW2. TheMBMS Session start response comprises and indication indicating that theMBMS Session start request in step 606 was ok.

Step 609

The MME/SGSN 1 checks the “MBMS IP Multicast Distribution” updated fromthe MBMS-GW1 to the MBMS-GW2, and triggers an M3 interaction to conveythis to the downstream nodes.

Step 610

This step corresponds to step 204 a in FIG. 2A. The MME/SGSN1 sends aMBMS Session Start Request to the MCE (eNB). The MBMS Session startrequest comprises a ‘Restoration flag’ for MBMS Session 1 and a GW2‘MBMS IP Multicast Distribution’.

Step 611

This step corresponds to step 205 a in FIG. 2A. The MCE (eNB) reads therestoration flag from step 610 so as to accept the MBMS Session StartRequest message received in step 610.

Step 612

This step corresponds to step 205 a in FIG. 2A. Due to M1 informationupdated from the MBMS-GW1 to the MBMS-GW2, the MCE (eNB) stops theexisting MBMS Session 1.

Step 613

This step corresponds to step 205 a in FIG. 2A. The MME/SGSN 1 startsthe MBMS Session 1 with the MBMS-GW2 M1 information.

Step 614

This step corresponds to step 206 a in FIG. 2A. The MCE (eNB) sends aMBMS Session Start Response to the MME/SGSN 1. The MBMS Session startresponse is a response to the MBMS Session start request in step 610.The MBMS Session start response comprises an indication indicating thatthe MBMS Session start request was ok.

Step 615

As a result of steps 601-614, MBMS Session 1 exists on BMSC, GW2, GW1,MME/SGSN1 (may be MME/SGSN2 as well) and the MCE(eNB). Note that theMBMS Session exists on both the old and new nodes!

FIG. 6B will now be described, which is a continuation of step 6 a sothat steps 601-615 has already been performed when starting with thefirst step 616 in FIG. 6B. FIG. 6B comprises steps 616-628, which stepsmay be performed in any suitable order than described below:

Step 616

This step corresponds to step 208 c in FIG. 2C. A MBMS Session update isperformed along the new control path. Subsequent Normal Handling on theprocedure required by MSG1.

For steps 617-622: If the old path is recovered, the upstream node thatchooses an alternative downstream node is responsible for clearing theMBMS Sessions on the nodes along the old path

Step 617

This step corresponds to step 208 b in FIG. 2B and step 209 c in FIG.2C. After the MBMS Session update has been performed, the path betweenthe BM-SC and the MBMS-GW1 is recovered.

Step 618

This step corresponds to step 209 b in FIG. 2B. The BM-SC Initiates aMBMS Session Stop towards the old path for those MBMS Sessions takenover by an alternative node. The BM-SC sends a RAR to the MBMS-GW1. TheRAR is a MBMS Session Stop Request for MBMS Session 1. The purpose ofthe MBMS Session stop request is to clear the MBMS Session along the oldpath.

Step 618 a

This step corresponds to step 215 c in FIG. 2C and is an alternative tostep 618. The MBMS-GW2 sends a MBMS session stop request to theMBMS-GW1. The MBMS session stop request comprises an indication toindicate that the delete is part of restoration procedure or a new GTPmessage for the same purpose to delete the MBMS session. This is inorder to clear the MBMS session on the nodes along the old path.

Step 619

This step corresponds to step 210 b in FIG. 2B. The MBMS-GW1 sends a RAAto the BM-SC in response to the RAR in step 618. The RAA comprise a MBMSSession Stop Response and indicates that the RAR was approved.

Step 619 a

This step corresponding to step 217 c in FIG. 2C and is an alternativeto step 619. The old MBMS-GW1 sends a session stop response or a new GTPmessage for the same purpose to the new MBMS-GW1 to acknowledge thereceipt of the request which was received in step 618.

Steps 620-622 below relates to the example where the MME/SGSN1 waschosen in the Restoration Phase.

Step 620

The MBMS-GW1 sends a MBMS Session stop request for MBMS Session 1 to theMME/SGSN 1.

Step 621

This step corresponds to step 211 b in FIG. 2B. The MME/SGSN 1 fails tomatch the MBMS Session due to that the GTP-C path has been updated toGW2.

Step 622

This step corresponds to step 211 b in FIG. 2B. The MME/SGSN 1 sends aMBMS Session Stop Response to the MBMS-GW 1. The MBMS Session stopresponse is a response to the MBMS Session stop request in step 620. TheMBMS Session stop response comprises an indication indicating that theMBMS Session stop request has failed.

Steps 623-627 below relates to the example where the MME/SGSN2 waschosen in Restoration Phase.

Step 623

This step corresponds to step 211 b in FIG. 2B. The MBMS-GW 1 sends aMBMS Session Stop Request for MBMS session 1 to the MME/SGSN 2.

Step 624

This step corresponds to step 211 b in FIG. 2B. The MME/SGSN 2 sends aMBMS Session Stop Response to the MBMS-GW 1. The MBMS Session stopresponse comprises an indication indicating that the MBMS Session stoprequest in step 623 was ok. The MBMS Session stop response is a responseto the MBMS Session stop request.

Step 625

This step corresponds to step 211 b in FIG. 2B. The MME/SGSN 2 sends theMBMS Session stop request for MBMS Session 1 to the MCE (eNB).

Step 626

This step corresponds to step 211 b in FIG. 2B. The MCE (eNB) fails tomatch the MBMS Session due to that the M3AP path was updated to theMME/SGSN 2.

Step 627

This step corresponds to step 211 b in FIG. 2B. The MCE (eNB) sends aMBMS Session stop response to the MME/SGSN 1. The MBMS Session stopresponse is a response to the request in step 625. The MBMS Session stopresponse comprises an indication indicating the failure in step 626.

Step 628

As a result of the steps above, MBMS Session 1 exists only on BMSC, GW2,MME/SGSNx (where x equals 1 or 2) and MCE (eNB). MBMS Session 1 therebyonly exists along the new path.

In FIGS. 2a, 2b and 2c above, the signaling sequence was described ingeneral. A signaling sequence for restoration in an example with a Sn/Smpath failure will now be described with reference to FIG. 7 and withreference to FIG. 4 illustrating the communications network 100 wherethe failure occurs. Sesssion 1 exist on BM-SC, GW, MME1 and MCE (eNB) atstart of the method. The method comprises the following steps, whichsteps may be performed in any suitable order than described below:

Step 701

A path failure occurs.

Step 702

The content provider sends a MBMS session update request for MBMSsession 1 to the BM-SC.

Step 703

The BM-SC sends a RAR to the MBMS-GW1. The RAR may be a MBMS sessionstart request comprising a restoration flag for MBMS session 1.

Step 704

The MBMS-GW1 sends a RAA to the BM-SC. The RAA may be a MBMS sessionstart response acknowledging the request received in step 703.

Step 705

The MBMS-GW1 chooses an alternative MME to restore the MBMS session 1.

Step 706

The MBMS-GW1 sends a MBMS session start request comprising a restorationflag for MBMS session 1 for to the MME/SGSN2.

Step 707

The MME/SGSN2 handles the MBMS session start request.

Step 708

The MME/SGSN2 sends a MBMS session start response to the MBMS-GW1acknowledging the received request in step 7067.

Step 709

The MME/SGSN2 sends a MBMS session start request comprising therestoration for MBMS session 1 to the MCE(eNB)/RNC.

Step 710

The MCE(eNB)/RNC reads the restoration flag and thereby accepts therequest message.

Step 711

The MCE(eNB)/RNC updates the M3AP path for the MBMS session 1 toMME/SGSN2.

Step 712

The MCE(eNB)/RNC sends a MBMS session start response to the MME/SGSN2 inorder to acknowledge the request received in step 709.

As a result of the steps 701-712, the MBMS session 1 exists on theBM-SC, the GW, the MME/SGSN1, the MME/SGSN2 and the MCE(eNB)/RNC. TheMBMS session exists on both the old and new MME/SGSN nodes.

Step 713

A MBMS session update occurs along the new control path. Subsequentnormal handling on the procedure required by MSG1.

Step 714

The path between the MBMS-GW1 and the MME/SGSN1 is recovered.

Step 715

The MBMS-GW1 initiates a MBMS session stop towards the old path forthose MBMS sessions taken over by the alternative/new node. The MBMS-GW1sends a RAR to the MME/SGSN1. The RAR may be a MBMS session stop requestfor MBMS session 1.

Step 716

The MME/SGSN1 sends a RAA to the MBMS-GW1. The RAA may be a MBMS sessionstop response comprising an acknowledgement for the request received instep 715.

Step 718

The MME/SGSN1 sends a MBMS session stop request for the MBMS session 1to the MCE(eNB)/RNC.

Step 719

The MCE(eNB)/RNC fails to match the MBMS session due to that M3AP pathhas been updated to MME/SGSN2.

Step 720

The MCE(eNB)/RNC sends a MBMS session stop response to the MME/SGSN1comprising information indicating that the request in step 718 hasfailed.

As a result of steps 714-720, the MBMS session 1 exists on BM-SC, theGW1, the MME/SGSN2 and the MCE(eNB)/RNC. The MBMS session only existsalong the new path. If the old path has been recovered, the upstreamnode who chooses an alternative downstream node is responsible forclearing the MBMS sessions on the nodes along the old path.

Restoration MBMS Session Along the New Nodes

During the restoration phase, i.e. steps 601-615 in FIG. 6B, analternative MBMS-GW (MBMS-GW2 in this example) is selected. Note thatthe MBMS Session still exists on the old MBMS-GW (MBMS-GW1 in thisexample) for the second alternative described in FIG. 2B.

From the GW2 perspective, the GW2 knows that this MBMS Session setup isfor restoration purpose from the restoration flag comprised in the MBMSSession start request message. The GW2 carries the restoration flag tothe downstream node as well during the MBMS Session setup procedure. TheGW2 may select the old downstream node (e.g. MME/SGSN1) or a newdownstream node (e.g. MME/SGSN2) to restore this MBMS Session:

In the case of the old MME/SGSN (e.g. MME/SGSN1) is selected by the GW2,the MME/SGSN1 knows that this is for restoration purpose from therestoration flag. As a result, the MME/SGSN1 accepts the new MBMSSession Start Request for the existing MBMS Session 1 from the new GW(e.g. GW2). Note that without the restoration flag, it is highly likelythat the MME/SGSN1 would reject the MBMS Session Start Request from anew GW as an error case.

By comparing the “MBMS IP Multicast Distribution” value in the comingmessage with the existing MBMS Session information, the MME/SGSN1understands that it must update its downstream nodes e.g. MCE(eNB) withthis information. So the MME/SGSN1 sends the MBMS Session Start Requestmessage towards the MCE/eNB with both the restoration flag and theupdated parameters carried.

Note: If all parameters in the coming message have the same value asthose in the existing MBMS Session, the MME/SGSN1 will only respond tothe GW2 with a successful MBMS Session start response message withoutfurther interacting with its downstream nodes.

In the case of a new MME/SGSN (e.g. MME/SGSN2) is selected by the GW2,the MME/SGSN2 gets a restoration flag in the MBMS Session Start Request.However, the MME/SGSN2 cannot locate the existing MBMS Session with theTMGI and Flow-ID. The MME/SGSN2 handles this MBMS Session Start Requestas a new MBMS Session setup and sends a MBMS Session Start Request tothe MCE/eNB but also with restoration flag set in M3 to help theMCE(eNB) differentiate the restoration procedure from others. Note thatthe MBMS Session still exists on the old MME/SGSN (MME/SGSN1).

Regardless of whether MBMS Session Start Request message is from the oldMME/SGSN or the new MME/SGSN, the MCE (eNB) accepts message after havingreceived the restoration flag. Because the “MBMS IP MulticastDistribution” changes, the MCE(eNB) stops the existing MBMS Session withthe old “MBMS IP Multicast Distribution” and then sets-up the MBMSSession with the new “MBMS IP Multicast Distribution”.

Until at this time point, the subsequent procedures originally requiredby the content provider 115 (e.g. MBMS Session Update or Stop) may befurther processed along the new control plane path.

Stop MBMS Session on the Old Nodes

As mentioned above, the MBMS session exists on both the GW1 and the GW2,and also possible in both the MME/SGSN1 and the MME/SGSN2 (if the GW2selects MME/SGSN2 when restoring this MBMS Session). This co-existenceis problematic in some cases so the old MBMS Session may be deleted assoon as possible. Apparently the proposal by using RESET with atake-over indication is not applicable for a SGmb path failure.

As shown in FIG. 6B, for the MBMS Session removal along the old path,once the path has been recovered, the upstream node (e.g. BM-SC in thiscase) who initiates restoration with reselection of the control node hasto inform the old node to delete the MBMS sessions have been taken overby others. The BM-SC sends a MBMS Session Stop Request towards the oldMBMS-GW (GW1). The GW1 who is not aware of the MBMS Session is taken bythe GW2 release its MBMS Session resource and stops the MBMS Sessiontowards the downstream nodes, e.g. MME/SGSN1, by sending a MBMS SessionStop Request to the MME/SGSN1. There are two possibilities forMME/SGSN1's behavior upon receiving this Stop Request according to theprevious restoration procedure outcome:

(1) If the restored MBMS Session is still on the MME/SGSN1, then theMME/SGSN1 has already changed the GTP-C path with the MBMS-GW from theGW1 to the GW2 during the MBMS Session restoration phase. So theMME/SGSN1 will not able to locate the MBMS Session required to bestopped by the GW1. Thus, the MME/SGSN rejects the request. The MBMSSession deletion procedure ends.

(2) If the restored MBMS Session goes on the MME/SGSN2, then theMME/SGSN1 is not aware of the MBMS Session is taken by the MME/SGSN2. Asa result, the MME/SGSN1 will send back a MBMS Session Stop Response witha successful cause and then continue to stop the MBMS Session by sendingthe MBMS Session Stop Request to its downstream nodes e.g. MCE(eNB).

Since the M3AP path on the MCE (eNB) has changed from the MME/SGSN1 tothe MME/SGSN2 during the restoration phase, the MCE (eNB) will not ableto match the MBMS Session along the old M3AP path so it rejects it. TheMBMS Session deletion procedure ends.

At this step, the MBMS Session on the old nodes is stopped. The MBMSSession exists normally on nodes along the new path.

The example embodiment of letting the upstream nodes to trigger MBMSSession stop procedure along old path is also valid for Sm/Sn pathfailure where it is the MBMS-GW who selects a new MME/SGSN may triggerthe MBMS Session stop once the path failure is recovered.

Impact Analysis for MBMS Session Coexistence Risk

Then coming back to the “risk” of the embodiments herein, i.e. both theold MBMS-GW/MME/SGSN and new MBMS-GW/MME/SGSN will have the same MBMSsession between the time when the MBMS session being taken over and thetime when the Sm/Sn/SGmb path is recovered, if we assume the restorationflag was introduced, the “risk” may be avoided. FIG. 8 exemplified theMBMS Session coexistence.

(i) Considering that a Sm failure has occurred between the MME/SGSN1 andthe MBMS-GW 1. if a subsequent M3AP path failure or MCE restart takesplace between the time when the MBMS session being taken over and thetime when the Sm/Sn is recovered, the new MME/SGSN may still include therestoration flag as it remembers that the MBMS session was started witha restoration flag. The old MME/SGSN may send a MBMS session startrequest message without any restoration flag. With this approach, theMBMS session 1 will continue to be handled by the new MME/SGSN 2 and theMBMS session 2 will be continued to be handled by the old MME/SGSN 1.

(ii) Considering that a SGmb failure has occurred between the MBMS-GW 1and the BM-SC and the BM-SC has selected the MBMS-GW 2 for the MBMSSession 1 and 2 upon receiving Update/Stop from the content provider115. If a subsequent Sm path failure takes place between the MME/SGSN 1and the MBMS-GW1 during the time when the MBMS session is being takenover and the time when the SGmb is recovered, but before the SGmb pathis recovered, the MBMS-GW will not trigger any re-selection of MME/SGSNas it cannot receive any MBMS session update or stop message.

(iii) Considering that a SGmb failure has occurred between the MBMS-GW 1and the BM-SC, and that the BM-SC has selected the MBMS-GW 2 for MBMSSession 1 and 2 upon receiving an Update message or a Stop message fromthe content provider 115. If a subsequent MME/SGSN1 restart takes placeand the MME/SGSN1 recovers before the Max SGmb path failure timerexpires, the MBMS-GW 1 will try to re-establish the MBMS Sessions 1, 2,3 and 4. Since there is no MME/SGSN reselection procedure, thecorresponding MBMS Session Start request messages will not comprise therestoration flag. At the same time, the MBMS-GW 2 will also re-establishMBMS session 1 with a restoration flag. Since the restoration flag wasincluded by the BM-SC when re-selecting the MBMS-GW2, the MME/SGSN1 mayaccept the one with the restoration flag from the MBMS-GW2. For the MBMSsession 2, as it is restored by the MME/SGSN2 with a restoration flag,the MCE may reject the corresponding MBMS Session start message from theMME/SGSN1 for MBMS session 2.

However, using Restoration flag need a time restraint, i.e. therestoration flag may be provided together with a guard timer, e.g. Maxnon-transient path failure timer in the node who initiatesrestoration—time elapse from the detection of path failure up to whenthe reselection of alternative control path, possibly plus an offsetbetween the timers configured in the different nodes, e.g. when there isa SGmb path failure and Max non-transparent failure timer in the BM-SCis 115 s, and when BM-SC decides to select another MBMS-GW at 20^(th)second since the path failure is detected, the restoration flag may beincluded with a timer 115 s−20 s+offset (between the timer in MBMS-GWand BM-SC, 120−115)=100 s.

So the restoration flag may be included as long as the associated timeris not expired when subsequent downstream failure takes place.

In addition, the restoration flag may be provided together with acounter. This is to solve the case when the subsequent same type of pathfailure takes place, for example, path failure between MBMS-GW1 andBM-SC, after 20 s, the BM-SC select alternative MBMS-GW 2 with avalidation timer 100 s (115 s−20+5), however at the 40th second, thelink between MBMS-GW 2 and BM-SC is failed, and at 60th second, the MME1restarts. Between 40 s−60 s, the BM-SC may select the third alternativeMBMS-GW 3? So the same MBMS session may exist in more than two controlpaths. When a counter is provided together with restoration flag, e.g.the BM-SC selects the third MBMS-GW3, it may increment the counter, thereceiver will only handle the request message with highest counter,which is the latest.

To perform the method steps shown in FIGS. 2 and 6 the network node 101comprises an arrangement as shown in FIG. 9. As mentioned above, thenetwork node 101 may be a BM-SC or a MBMS-GW. The network node 101comprises a receiver 901 adapted to receive messages from e.g. a contentprovider 115 and control plane nodes 103. The network node 101 furthercomprises a transmitter 903 adapted to transmit messages to e.g. thecontent provider 115 and control plane nodes 103. The network node 101may further comprise a memory 905 comprising one or more memory units.The memory 905 is arranged to be used to store data, received datastreams, timers, messages, information related to MBMS sessions,information related to paths, threshold values, time periods,configurations, schedulings, and applications to perform the methodsherein when being executed in the network node 101. Those skilled in theart will also appreciate that the receiver 901 and the transmitter 903described above may refer to a combination of analog and digitalcircuits, and/or one or more processors configured with software and/orfirmware, e.g. stored in the memory 905, that when executed by the oneor more processors such as the processor 910 perform as described above.

To perform the method steps shown in FIGS. 2 and 6 the control planenode 103 comprises an arrangement as shown in FIG. 10. The control planenode 103 may be an old or a new control plane node. As mentioned above,the control plane node 103 may be a MBMS-GW or a MME/SGSN. The controlplane node 103 comprises a receiver 1001 adapted to receive messagesfrom e.g. a network node and other control plane nodes. The controlplane node 103 further comprises a transmitter 1003 adapted to transmitmessages to e.g. the network node and other control plane nodes. Thecontrol plane node 103 may further comprise a memory 1005 comprising oneor more memory units. The memory 1005 is arranged to be used to storedata, received data streams, timers, messages, information related toMBMS sessions, information related to paths, threshold values, timeperiods, configurations, schedulings, and applications to perform themethods herein when being executed in the control plane node 103. Thoseskilled in the art will also appreciate that the receiver 1001 and thetransmitter 1003 described above may refer to a combination of analogand digital circuits, and/or one or more processors configured withsoftware and/or firmware, e.g. stored in the memory 1005, that whenexecuted by the one or more processors such as the processor 1010perform as described above.

To perform the method steps shown in FIGS. 2 and 6 the RAN node 105comprises an arrangement as shown in FIG. 11. As mentioned above, theRAN node 105 may be a base station, eNB, NB, RNC, MCE, MSC etc. The RANnode 105 comprises a receiver 1101 adapted to receive messages from e.g.the new and/or old control plane node 103 a,b and other control planenodes. The RAN node 105 further comprises a transmitter 1103 adapted totransmit messages to e.g. the new and/or old control plane node 103 a,band other control plane nodes. The RAN node 105 may further comprise amemory 1105 comprising one or more memory units. The memory 1105 isarranged to be used to store data, received data streams, timers,messages, information related to MBMS sessions, information related topaths, threshold values, time periods, configurations, schedulings, andapplications to perform the methods herein when being executed in theRAN node 105. Those skilled in the art will also appreciate that thereceiver 1101 and the transmitter 1103 described above may refer to acombination of analog and digital circuits, and/or one or moreprocessors configured with software and/or firmware, e.g. stored in thememory 1105, that when executed by the one or more processors such asthe processor 1110 perform as described above.

The present mechanism for handling MBMS sessions in a communicationsnetwork may be implemented through one or more processors, such as aprocessor 910 in the network node 101 depicted in FIG. 9, a processor1010 in the control plane node 103 depicted in FIG. 10 and a processor1110 in the RAN node 105 depicted in FIG. 11, together with computerprogram code for performing the functions of the embodiments herein. Theprocessor may be for example a Digital Signal Processor (DSP),Application Specific Integrated Circuit (ASIC) processor,Field-programmable gate array (FPGA) processor or microprocessor. Theprogram code mentioned above may also be provided as a computer programproduct, for instance in the form of a data carrier carrying computerprogram code for performing the embodiments herein when being loadedinto the network node 101 and/or control plane node 103 and/or RAN node105. One such carrier may be in the form of a CD ROM disc. It is howeverfeasible with other data carriers such as a memory stick. The computerprogram code may furthermore be provided as pure program code on aserver and downloaded to the network node 101 and/or control plane node103 and/or RAN node 105.

Thus, in an embodiment, a computer program comprising computer programcode is provided for causing the network node 101 to perform one or moreembodiments previously discussed, when the computer program code isexecuted on the processor 910 included in the network node 101.

In a further embodiment, a computer program comprising computer programcode is provided for causing the new, alternative control plane node 103b to perform one or more embodiments previously discussed, when thecomputer program code is executed on the processor 1010 included in thenew control plane node 103 b.

In still a further embodiment, a computer program comprising computerprogram code is provided for causing the RAN node 105 to perform one ormore embodiments previously discussed, when the computer program code isexecuted on the processor 1110 included in the RAN node 105.

In yet a further embodiment, a computer program product comprising thepreviously mentioned data carrier having the computer program accordingto the mentioned embodiments embodied therein.

Some embodiments herein introduce a restoration flag to be set by thenode who initiates restoration procedure with re-selection of downstreamcontrol node.

It is also described that it may be required for the node who initiatesrestoration with re-selection of downstream control node to inform theold node to stop the MBMS session which have been taken over by othersafter a transient path failure is recovered.

It is also described that the receiving node may use the restorationflag to decide which MBMS Session Start message may be accepted for thecase that the same MBMS session is controlled by two different controlplan node, e.g. MME/SGSN/MBMS-GW.

It is also described how to configure the Max path failure timer inMME/SGSN<in MBMS-GW<in BM-SC in order to re-establish the MBMS Sessionbefore bring it down. The difference between these timers may be kept asreasonable low.

It is described above how to use the restoration flag to avoid differentproblems.

It is also described that the node who initiates restoration withre-selection of downstream node to inform the old downstream node tostop the MBMS session which have been taken over by other node.

It is described above to introduce a restoration flag to be set by thenode who initiates restoration procedure with re-selection of downstreamcontrol node, e.g. BM-SC selects an alternative MBMS-GW, together with atimer and a counter.

The timer may be set to the Max non-transient path failure timer node inthe node (who initiates the restoration procedure) minus the timeelapses since the path failure is detected up to the moment when thereselection of alternative control path and plus the difference betweenthe Max non-transient path failure in the node (who initiates therestoration procedure) and next downstream node. The counter incrementsif there is a subsequent path failure.

The restoration flag may be included as long as the associated timer isnot expired when subsequent downstream failure takes place.

It is also described to require the node who initiates restoration withre-selection of downstream control node to inform the old node to stopthe MBMS session which have been taken over by others after a transientpath failure is recovered.

It is also described that the receiving node may use restoration flag todecide which MBMS Session Start message may be accepted for the casethat the same MBMS session is controlled by two or more differentcontrol plan nodes, e.g. MME/SGSN/MBMS-GW.

In the embodiments herein, the whole solution on restoring a MBMSSession is presented by describing the node behaviors clearly uponvarious combinations of the restoration flag (a new flag over SGmb (3GPPTS 29.061), Sm/Sn (to be added in 3GPP TS 29.274), M3, M2 and Iuinterface (to be added in 3GPP TS 25.413)) and other parameters. Morespecifically, for the scenario described in FIG. 2, the behavior ofMME/SGSN is addressed with “MBMS IP Multicast Distribution” updated ornot in the MBMS Session Start Request message with a restoration flag.

The restoration flag may clearly tell the receiver (e.g. MME/SGSN) thisis a restoration procedure for the very same MBMS service identified byTMGI and Flow-ID.

If the same downstream node, i.e., MME/SGSN1, is selected during therestoration procedure, by comparing the “MBMS IP Multicast Distribution”with the existing MBMS Session information, MME/SGSN1 may get to knowthe Control information for the M1 interface changes or not. If itchanges, then MME/SGSN must convey this updated information to eNBs. Ifit does not change, the M3 interaction is not needed if all otherparameters are the same.

If a different downstream node, i.e., MME/SGSN2, is selected, then bothold node and new node will have the same MBMS session, the embodimentsherein propose to stop the resource on the old control path by theupstream node (e.g. BM-SC who selects a new MBMS-GW in case of SGmb pathfailure, or MBMS-GW who selects a new MME/SGSN in case of Sm pathfailure) after the old path is recovered.

The embodiments herein describe MBMS Session restoration towards analternative downstream node procedure for the case of SGmb pathtransient failure. The embodiments herein also describe a MBMS Sessionstop procedure towards the old downstream node for case of SGmb/Sm/Snpath transient failure.

The control path may be re-established to allow subsequent MBMS sessionupdate and stop; in addition, such re-establishing may be performedbefore bring down the MBMS sessions.

The embodiments herein are not limited to the above describedembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the embodiment.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components, but does not preclude thepresence or addition of one or more other features, integers, steps,components or groups thereof. It should also be noted that the words “a”or “an” preceding an element do not exclude the presence of a pluralityof such elements. The term “configured to” used herein may also bereferred to as “arranged to” or “adapted to”.

It should also be emphasised that the steps of the methods defined inthe appended claims may, without departing from the embodiments herein,be performed in another order than the order in which they appear.

Some embodiments described herein may be summarized as follows.

One embodiment relates to a method in a network node for restoring anMBMS session after path failure, comprising: detecting a path failureassociated with an old path between the network node and an old controlplane node, which old control plane node controls at least one MBMSsession; selecting the new, alternative control plane node tore-establish the at least one MBMS session; detecting that the old pathbetween the network node and the old control plane node has beenrecovered; and sending to the old control plane node an MBMS sessionstop request in order to clear the MBMS session on the nodes along theold path involving the old control plane node.

The method may further comprise detecting that the path failure is atransient path failure.

The method may further comprise performing the selecting before a pathfailure timer has expired.

Further, in the method, the path failure may be regarded as transientwhen the selection takes place before the path failure timer hasexpired.

The method may further comprise: sending an MBMS session start requestto the new control plane node; and receiving an MBMS session startresponse from the new control plane node acknowledging the receipt ofthe MBMS session start request.

Further, in the method, the MBMS session start request may comprise are-establishment flag enabling the new control plane node todifferentiate the restoration procedure from other procedures.

Further, in the method, the MBMS session start request may comprise are-establishment flag enabling the new control plane node todifferentiate whether it is an error so it may reject the MBMS sessionstart request, or whether it is a restoration procedure so it may acceptthe MBMS session start request.

Further, in the method, the MBMS session start request may comprise acounter enabling handling of a latest MBMS session start request in casea subsequent same type of path failure takes place.

The method may further comprise: receiving an MBMS session stop responsefrom the old control plane node.

Another embodiment relates to a method in a new, alternative controlplane node for restoring an MBMS session after path failure, comprising:receiving an MBMS session start request from the network node; sendingan MBMS session start request to the RAN node, possibly in the form ofor comprising an MCE; receiving an MBMS session start response from theRAN node; and sending an MBMS session start response to the network nodeacknowledging the receipt of the MBMS session start request.

Further, in the method, the MBMS session start request sent to the RANnode may comprise a re-establishment flag enabling the RAN node todifferentiate the restoration procedure from other procedures.

Further, in the method, the MBMS session start request sent to the RANnode may comprise a re-establishment flag enabling the RAN node to knowthat it may accept the MBMS session start request.

Further, in the method, the MBMS session start request sent to the RANnode may comprise a re-establishment flag enabling the RAN node todifferentiate whether it is an error so it may reject the MBMS sessionstart request or whether it is a restoration procedure so it may acceptthe MBMS session start request.

Further, in the method, the MBMS session start request may comprise acounter enabling handling of a latest MBMS session start request in casea subsequent same type of path failure takes place.

Another embodiment relates to a method in a RAN node, possibly in theform of or comprising an MCE, for restoring an MBMS session after pathfailure where the MBMS session already exists on the RAN node, themethod comprising: receiving an MBMS session start request comprising are-establishment flag for the MBMS session from the new control planenode; and re-establishing the MBMS session with the new control planenode.

The method may further comprise: sending a session start response to thenew control plane node 103 b acknowledging the receipt of the MBMSsession start request.

Further, in the method, the re-establishing may comprise: stopping theexisting MBMS session; and starting the MBMS session with the newcontrol plane node.

Further, in the method, the RAN node may use the re-establishment flagto differentiate the restoration procedure from other procedures.

Further, in the method, the RAN node may use the re-establishment flagto know that it may accept the MBMS session start request.

Further, in the method, the RAN node may use the re-establishment flagto differentiate whether it is an error so it may reject the MBMSsession start request or whether it is a restoration procedure so it mayaccept the MBMS session start request.

Further, in the method, the MBMS session start request may comprise acounter enabling handling of a latest MBMS session start request in casea subsequent same type of path failure takes place.

Another embodiment relates to a network node being configured to restorean MBMS session after path failure, comprising a processor and a memory.The memory contains software that when executed by the processor causesthe network node to be operative to: detect a path failure associatedwith an old path between the network node and the old control planenode, which old control plane node controls at least one MBMS session;select a new, alternative control plane node to re-establish the atleast one MBMS session; detect that the old path between the networknode and the old control plane node has been recovered; and send to theold control plane node an MBMS session stop request in order to clearthe MBMS session on the nodes along the old path involving the oldcontrol plane node.

The network node may further be operative to detect that the pathfailure is a transient path failure.

The network node may further be operative to select the alternativecontrol plane node 103 b before a path failure timer has expired.

The network node may further be operative to regard the path failure astransient when the selection takes place before the path failure timerhas expired.

The network node may further be operative to: send an MBMS session startrequest to the new control plane node; and receive an MBMS session startresponse from the alternative control plane node acknowledging thereceipt of the MBMS session start request.

The network node may further be operative to send the MBMS session startrequest comprising a re-establishment flag enabling the alternativecontrol plane node to differentiate the restoration procedure from otherprocedures.

The network node may further be operative to send the MBMS session startrequest comprising a re-establishment flag enabling the alternativecontrol plane node to differentiate whether it is an error so it mayreject the MBMS session start request, or whether it is a restorationprocedure so it may accept the MBMS session start request.

The network node may further be operative to send the MBMS session startrequest comprising a counter enabling handling of a latest MBMS sessionstart request in case a subsequent same type of path failure takesplace.

The network node may further be operative to receive an MBMS sessionstop response from the old control plane node.

The network node may be one of a BM-SC and a MBMS-GW.

Another embodiment is directed to a new alternative control plane nodeconfigured to restore a MBMS session after path failure. The controlplane node comprises a processor and a memory, said memory containingsoftware that when executed by said processor, the control plane node isoperative to: receive an MBMS session start request from a network node;send an MBMS session start request to a MCE; receive an MBMS sessionstart response from the MCE; and send an MBMS session start response tothe network node acknowledging the receipt of the MBMS session startrequest.

The control plane node may be further operative to send the MBMS sessionstart request to the MCE comprising a re-establishment flag enabling theMCE to differentiate the restoration procedure from other procedures.

The control plane node may be further operative to send the MBMS sessionstart request to the MCE comprising a re-establishment flag enabling theMCE to know that it may accept the MBMS session start request.

The control plane node may be further operative to send the MBMS sessionstart request to the MCE comprising a re-establishment flag enabling theMCE to differentiate whether it is an error so it may reject the MBMSsession start request or whether it is a restoration procedure so it mayaccept the MBMS session start request.

The control plane node may be further operative to send the MBMS sessionstart request comprising a counter enabling handling of a latest MBMSsession start request in case a subsequent same type of path failuretakes place.

The control plane node (103 b) according to any one of claims 32-36,said network node being one of: a Mobility Management Entity, MME, aServing General Packet Radio Service, GPRS, Support Node, SGSN, and aMultimedia Broadcast Multicast Service Gateway, MBMS-GW.

Still another embodiment relates to the RAN node, possibly in the formof or comprised by an MCE, being configured to restore an MBMS sessionafter path failure where the MBMS session already exists on the RANnode, comprising a processor and a memory. The memory contains softwarethat when executed by the processor causes the RAN node to be operativeto: receive an MBMS session start request comprising a re-establishmentflag for the MBMS session from the new control plane node; andre-establish the MBMS session with the alternative control plane node.

The RAN node may further be operative to: send a session start responseto the new control plane node acknowledging the receipt of the MBMSsession start request.

The RAN node may further be operative to: stop the existing MBMSsession; and start the MBMS session with the new control plane node 103b.

The RAN node may further be operative to use the re-establishment flagto differentiate the restoration procedure from other procedures.

The RAN node may further be operative to use the re-establishment flagto know that it may accept the MBMS session start request.

The RAN node may further be operative to use the re-establishment flagto differentiate whether it is an error so it may reject the MBMSsession start request or whether it is a restoration procedure so it mayaccept the MBMS session start request.

The RAN node may be one an RBS an eNB, a NodeB, a B node, an RNC, a BSC,and a BTS.

1. A method in a control plane node for restoring a Multimedia BroadcastMulticast Service (MBMS) session after path failure, comprising:receiving an MBMS session start request from a network node; sending anMBMS session start request to a Multi-cell/Multicast CoordinationEntity, MCE; receiving an MBMS session start response from the MCE; andsending an MBMS session start response to the network node acknowledgingthe receipt of the MBMS session start request.
 2. The method of claim 1,wherein the MBMS session start request sent to the MCE comprises are-establishment flag enabling the MCE to differentiate the restorationprocedure from other procedures.
 3. The method of claim 1, wherein theMBMS session start request sent to the MCE comprises a re-establishmentflag enabling the MCE to know that it may accept the MBMS session startrequest.
 4. The method of claim 1, wherein the MBMS session startrequest sent to the MCE comprises a re-establishment flag enabling theMCE to differentiate whether it is an error so it may reject the MBMSsession start request or whether it is a restoration procedure so it mayaccept the MBMS session start request.
 5. The method of claim 2, whereinthe MBMS session start request comprises a counter enabling handling ofa latest MBMS session start request in case a subsequent same type ofpath failure takes place.
 6. A method in a Multi-cell/MulticastCoordination Entity (MCE) for restoring a Multimedia Broadcast MulticastService (MBMS) session after path failure where the MBMS session alreadyexists on the MCE, the method comprising: receiving a MBMS session startrequest comprising a re-establishment flag for the MBMS session from analternative control plane node; and re-establishing the MBMS sessionwith the alternative control plane node.
 7. The method of claim 6,comprising: sending a session start response to the alternative controlplane node acknowledging the receipt of the MBMS session start request.8. The method of claim 6, wherein the re-establishing comprises:stopping the existing MBMS session; and starting the MBMS session withthe alternative control plane node.
 9. The method of claim 6, whereinthe MCE uses the re-establishment flag to differentiate the restorationprocedure from other procedures.
 10. The method of claim 6, wherein theMCE uses the re-establishment flag to know that it may accept the MBMSsession start request.
 11. The method of claim 6, wherein the MCE usesthe re-establishment flag to differentiate whether it is an error so itmay reject the MBMS session start request or whether it is a restorationprocedure so it may accept the MBMS session start request.
 12. Themethod of claim 6, wherein the MBMS session start request comprises acounter enabling handling of a latest MBMS session start request in casea subsequent same type of path failure takes place.
 13. A control planenode configured to restore a Multimedia Broadcast Multicast Service(MBMS) session after path failure, comprising a processor and a memory,said memory containing software that when executed by said processor,the control plane node is operative to: receive an MBMS session startrequest from a network node; send an MBMS session start request to aMulti-cell/Multicast Coordination Entity, MCE; receive an MBMS sessionstart response from the MCE; and send an MBMS session start response tothe network node acknowledging the receipt of the MBMS session startrequest.
 14. The control plane node of claim 13, wherein the controlplane node is operative to send the MBMS session start request to theMCE comprising a re-establishment flag enabling the MCE to differentiatethe restoration procedure from other procedures.
 15. The control planenode of claim 13, wherein the control plane node is operative to sendthe MBMS session start request to the MCE comprising a re-establishmentflag enabling the MCE to know that it may accept the MBMS session startrequest.
 16. The control plane node of claim 13, wherein the controlplane node is operative to send the MBMS session start request to theMCE comprising a re-establishment flag enabling the MCE to differentiatewhether it is an error so it may reject the MBMS session start requestor whether it is a restoration procedure so it may accept the MBMSsession start request.
 17. The control plane node of claim 13, whereinthe control plane node is operative to send the MBMS session startrequest comprising a counter enabling handling of a latest MBMS sessionstart request in case a subsequent same type of path failure takesplace.
 18. The control plane node of claim 13, said network node beingone of: a Mobility Management Entity, MME, a Serving General PacketRadio Service, GPRS, Support Node, SGSN, and a Multimedia BroadcastMulticast Service Gateway, MBMS-GW.
 19. A Multi-cell/MulticastCoordination Entity (MCE) configured to restore a Multimedia BroadcastMulticast Service (MBMS) session after path failure where the MBMSsession already exists on the MCE, comprising a processor and a memory,said memory containing software that when executed by said processor,the MCE is operative to: receive a MBMS session start request comprisinga re-establishment flag for the MBMS session from an alternative controlplane node; and re-establish the MBMS session with the alternativecontrol plane node.
 20. The MCE of claim 19, further being operative to:send a session start response to the alternative control plane nodeacknowledging the receipt of the MBMS session start request.
 21. The MCEof claim 19, further being operative to: stop the existing MBMS session;and start the MBMS session with the alternative control plane node. 22.The MCE of claim 19, wherein the MCE is operative to use there-establishment flag to differentiate the restoration procedure fromother procedures.
 23. The MCE of claim 19, wherein the MCE is operativeto use the re-establishment flag to know that it may accept the MBMSsession start request.
 24. The MCE of claim 19, wherein the MCE isoperative to use the re-establishment flag to differentiate whether itis an error so it may reject the MBMS session start request or whetherit is a restoration procedure so it may accept the MBMS session startrequest.
 25. The MCE of claim 19, wherein the MBMS session start requestcomprises a counter enabling handling of a latest MBMS session startrequest in case a subsequent same type of path failure takes place.